Inventor’s corner: Mini circuits

27 July 2012

Dr William (Tom) Pike is a Reader in Microengineering (Electrical and Electronic Engineering). His recent project focuses on increasing integration within three- dimensional circuits, whereby multiple layers of electronic components are incorporated into a single circuit. If more components were integrated into one circuit, devices such as printed circuit boards used in PCs could be made smaller, meeting the continuous push for miniaturisation.

What have you developed?

We have been using a machine called a deep reactive-ion etcher to carve precise holes through silicon wafers. We inject liquefied metal solder into the holes to produce a conductive pathway through the wafer connecting devices on each side. These vertical connections mean we can produce stacks of devices.

What challenges have you faced?

We are trying to make the holes small enough to produce the interconnects for micromachined Mini circuits inventor’s corner sensors, and getting the solder into them is challenging. We use surface tension, as well as gas pressure, to produce a force strong enough to push the liquid solder through the tiny holes. And to make the solder flow, we have had to work in a controlled atmosphere – replacing the air with nitrogen – to prevent oxidisation.

How is this innovative?

The strength of our invention is melting very small balls of solder and using surface tension to direct their flow. With this, we can take various chips that have gone through different processing routes and stack them together. This has been done before, on an individual level, but using the ion etcher and molten solder gives a more reliable and accessible method that can be mass produced.